1. Field of the Invention
One or more embodiments of the present invention relate to a negative active material and a lithium battery including the negative active material.
2. Description of the Related Art
Lithium secondary batteries used in portable electronic devices for information communication, such as PDAs, mobile phones, or notebook computers, electric bicycles, electric vehicles, or the like have a discharge voltage that is at least twice as high as that of a conventional battery and thus have high energy density.
Lithium secondary batteries generate an electric energy due to oxidation and reduction reactions occurring when lithium ions are intercalated into/deintercalated from a positive electrode and a negative electrode, each including an active material that enables intercalation and deintercalation of lithium ions, with an organic electrolytic solution or a polymer electrolytic solution interposed between the positive electrode and the negative electrode.
As a positive active material for lithium secondary batteries, for example, an oxide that includes lithium and transition metal and has a structure enabling intercalation of lithium ions may be used, and examples of such an oxide are a lithium cobalt oxide (LiCoO2), a lithium nickel oxide (LiNiO2), a lithium nickel cobalt manganese oxide (Li[NiCoMn]O2 or Li[Ni1-x-yCoxMy]O2), etc.
As a negative active material, studies on a carbonaceous material and a non-carbonaceous material, which enable intercalation or deintercalation of lithium ions, are being performed. Examples of a carbonaceous material are artificial and natural graphite, and hard carbon. An example of a non-carbonaceous material is Si.
A non-carbonaceous material has very high capacity that is 10 times greater than that of graphite. Electric conductivity of the non-carbonaceous material is, however, low, and during charging and discharging lithium, the non-carbonaceous material may volumetrically expand or shrink, and thus, its capacity retention rate, charge/discharge efficiency, and lifetime characteristics may be degraded. Accordingly, there is a need to develop a highly performing negative active material with improved efficiency and lifetime characteristics due to control on volumetric expansion.